The present invention relates generally to welding systems, and more particularly to a technique for advancing a wire electrode in a welding gun.
A wide range of welding techniques have been developed and are presently in use. Arc welding is a prominent and important class of welding in which an electric arc is established between a welding electrode and a work piece. The arc generally results from electrical power supplied to the electrode from a welding power supply. The power supply channels welding current to a welding gun or torch in which the electrode is placed. The gun is coupled to a cable that extends back to the power supply. The work piece is typically grounded, or at a polarity opposite that of the electrode. As the electrode is approached closely to or contacts the work piece, and arc is established that produces heat needed for melting either the work piece or the electrode or both.
One type of arc welding is generally referred to as metal inert gas (MIG) welding. In MIG welding, a continuous wire electrode is fed from a spool to the welding gun and from a tip of the welding gun to the location where the arc is established. The electrode is charged, such that the arc is established between the advancing wire electrode and the work piece. In many applications, an inert gas is also channeled to the welding gun tip to surround the weld and protect the weld both while the weld joint is molten and during solidification of the weld. Other wire electrode welding techniques do not use such gasses, but may rely upon a flux core within the wire electrode.
In welding applications employing wire electrodes, a challenge consists in driving the electrode toward the welding gun tip in a controlled and predictable manner. Current technologies for driving wire electrodes include driving one or more rollers that capture the continuous wire electrode therebetween, and drive the electrode towards the tip. The rollers are often positioned in the welding gun or handle itself, and a small drive motor powers a drive roller to advance the electrode, which is sandwiched between the moving rollers.
One difficulty in such arrangements is the need to provide the proper force or pressure on the electrode positioned between the rollers. Different sizes and types of wire electrode are available, and these typically require different roll pressures. For example, hand-held motorized welding torches may be used to feed relatively soft aluminum wire electrode (e.g., 4000 series), and also relatively harder aluminum wire electrodes (e.g., 5000 series) in a single handle arrangement. The softer electrodes require less roll pressure than the harder electrodes. If the roll pressure is too low, the wire electrode may seize in the contact tip of the torch. Excessive roll pressure, on the other hand, may cause the wire to be bent or wavy as it exits the contact tip. This waviness may complicate the welding operation by providing a relatively unpredictable location in which the electrode will contact the work piece. Electrode roll pressure is particularly problematic in pulsed MIG welding, where the harder aluminum wire electrode with an excessively low roll pressure will tend to withdraw an arc into the tip, and excessively high pressures will cause the electrode to drive through the point where the arc is concentrated, bending the wire.
Current approaches to adjustment of the roll pressure for motorized hand-held continuous electrodes basically rely upon trial and error in the adjustment process. The operator typically has little or no feedback from the device as to the level of pressure being applied on the electrode. Consequently, improper roll pressure in such applications is a continuing problem.
There is a need, therefore, for an improved technique for controlling roll pressure for advancement for continuous wire electrodes for welding applications. There is a particular need for a technique that provides user feedback and facilitates the adjustment operation when the nature of the electrode demands such adjustment.